The present invention is for a temperature control system and is more particularly directed to such systems utilizing more than one temperature probe for accurately controlling the temperature within a given area.
The problem of accurately controlling temperatures within an enclosure is an old one. If a temperature controlling thermostat is placed near a heating/cooling source, desirable fast response times are obtained for modulating the heating/cooling source. However, at the same time, the actual temperature within much of the enclosure (e.g. at its geometrical mean) differs from the thermostat set point. The amount of this differernce is sometimes called "droop" or "offset" and it varies with changes in the thermal load presented to the system. For example, in an incubator enclosure, droop may increase significantly for a time after the enclosure is opened and an object is inserted having a much different temperature from the ambient incubator temperature. This invention is directed to the substantial solution of this problem by the use of interactive dual temperature probes employed at different locations within the same enclosure. These probes are used to actually measure the existing droop associated with the probe used to control the heating/cooling source and to automatically adjust its set point so as to more accurately maintain the actually desired temperature with changing thermal loads.
Temperature control systems utilizing more than one temperature probe are well known in the art. The temperature information measured by such plural temperature probes has been utilized in a variety of ways as illustrated by the following U.S. Pat. Nos.:
4,189,093 Schnaibel et al PA0 4,089,462 Bradford PA0 3,768,545 Wills PA0 3,761,018 Rekai PA0 3,724,534 Weatherston PA0 3,450,862 Kralovec, Jr. PA0 3,408,004 Miller PA0 3,112,791 Brahm PA0 2,572,293 Wilson et al PA0 2,451,566 Lehane et al
In certain of the prior art references, such as the Bradford and Rekai references, one thermostat is placed inside and one thermostat is placed outside of the area which is to be temperature controlled. The thermostat inside the area of interest is used to control a heat source. The thermostat outside of the area of interest is used to monitor the outside ambient temperature. In response to changes in the outside ambient temperature, the output point of the inside thermostat is supplemented to compensate for detected changes in the outside temperature.
Prior art multiple probe temperature control systems often utilize plural temperature probes to obtain an average temperature. Such a system is disclosed in U.S. Pat. No. 2,572,293. A similar utilization of the signals produced by the temperature probes is illustrated in U.S. Pat. No. 3,724,534 wherein the amount of heating and cooling supplied is controlled by an electronic scanning system which periodically samples each of the zone thermostats. The overall heating and cooling means is adjusted according to the sum of the zone requirements.
It is also known in the prior art to use two temperature sensors each for controlling the operation of a heat source as illustrated in U.S. Pat. Nos. 3,450,862 and 2,451,566. Prior art temperature control systems also utilize multiple temperature sensors in a variety of other ways. In U.S. Pat. No. 4,189,093 three temperature sensors are utilized. Two are connected in series, one insulated and one uninsulated, so as to provide a dynamic, sensitive and accurate measurement of the temperature in the area near the heat source. In U.S. Pat. No. 3,768,545 a first thermostat is located in the discharge air passage and a second thermostat is located in the return air passage. A selection circuit energizes one of the thermostats below a preset temperature and the other thermostat above the preset temperature. In this manner, only one of the thermostats is operative at a time. In U.S. Pat. No. 3,408,004 a low and high thermostat control the heat supplied to a source of hot water. A space thermostat controls the heat supplied to the monitored space while a water thermostat monitors the overall water temperature. In U.S. Pat. No. 3,112,791 two temperature probes are utilized, one to turn the heat source off and on and one to limit the rate of change of the air temperature in a supply duct.
As can be seen, prior art temperature control systems utilizing more than one temperature sensor are well known. The prior art systems utilize the temperature sensors in a variety of ways including at least those discussed above. However, none is believed to teach or suggest my unique and advantageous arrangement of interactive dual temperature probes employed at different locations within the same enclosure so as to measure the actual "droop" parameter associated with the probe used to control heating/cooling and to automatically adjust its set point so as to more accurately maintain the actually desired temperature with changing thermal loads.